A hybrid vehicle having an internal combustion engine, a rotary electric machine, and an electric charge storage device is known. The engine and the rotary electric machine are the drive power generators that generate drive power for driving the drive shaft of the vehicle. The electric charge storage device supplies the rotary electric machine with electric power for rotating the machine.
Because a hybrid vehicle has two types of drive power generators, it is possible to improve the fuel consumption rate of the vehicle by properly transferring the drive power generated by the generators. Therefore, the drive power transfer for the two types of drive power generators is important. By way of example, the drive power transfer may be determined by using the travel route set by a navigation unit disclosed in Patent Document 1 (Japanese Patent No. 3,610,879).
In Patent Document 1, while the vehicle is traveling actually along a travel route, charge and discharge control of a battery is so performed as to satisfy a target charging rate based on a predicted traveling pattern. However, not all the actual traveling patterns during the traveling are the same as the predicted patterns. As a result; the battery charging time point and the battery discharging time point may not be optimal. For example, even when electric power is generated at the time point at which the electric power generation efficiency is predicted to be high, the electric power generation may occur actually when the electric power generation efficiency is low.
In Patent Document 2 (JP 2008-183937 A), a proposed travel route for a vehicle and the drive power for the route are predicted. The proposed travel route is divided into sections. For each of the route sections, an electric power generation cost is computed as an index of the fuel increase caused by the electric power generation when the vehicle travels in an electric power generation mode. Likewise, for each of the route sections, an electric assist cost is computed as an index of the fuel decrease caused by the drive power assistance of the rotary electric machine of the vehicle when the vehicle travels in a drive power assist mode. Based on the electric power generation cost and the electric assist cost, an electric power generation cost reference value and an electric assist cost reference value are set as references for the electric power generation cost and the electric assist cost, respectively. An actual electric power generation cost and an actual electric assist cost are computed from the actual demanded drive power demanded by the axel of the vehicle, etc. While the vehicle is traveling, the drive power generated by the internal combustion engine of the vehicle and the electric power generated by the rotary electric machine or the assist electric power from the machine are controlled based on the actual electric power generation cost and the electric assist cost, the electric power generation cost reference value, and the electric assist cost reference value.
In Patent Document 2, the electric power generation and the assistance are controlled based on the electric power generation cost reference value and the electric assist cost reference value. This can avoid the problem with Patent Document 1 that charging and discharging time point deviations may cause inefficient electric power generation and drive power assistance. However, in the invention of Patent Document 2, only one future traveling pattern is predicted, and the electric power generation cost reference value and the electric assist cost reference value are set based on the pattern. As a result, when the speed of the vehicle and the drive power vary greatly when the vehicle travels at different times along the travel route, the set value of the electric power generation or the assist electric power is not always the optimum value, so that it may not be possible to sufficiently improve the fuel consumption rate.